JP2011020867A - Method for selecting fly ash and method for producing cement using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for selecting a fly ash wherein a fly ash which is suitable for producing cement having stably good strength development is selected as a cement admixture. <P>SOLUTION: The method for selecting a fly ash is characterized by selecting from one or more kinds of fly ashes containing α-quartz, a fly ash having a BET specific surface area of 5.0 m<SP>2</SP>/g or less and a lattice constant b of the α-quartz obtained by Rietveld analysis of 0.4935 nm or less as a cement admixture. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a selection method for selecting fly ash capable of improving the strength development of cement and the selected fly ash in utilizing fly ash generated in a thermal power plant or the like as a cement mixture. The present invention relates to a method for producing a mixed cement.

  Fly ash (coal ash) is obtained by collecting fine coal ash in the combustion gas of a boiler with an electric dust collector or the like in a thermal power plant using coal as fuel. Since this fly ash is usually spherical particles, it is used as a cement mixture or a concrete aggregate for the purpose of improving fluidity. The concrete obtained by adding fly ash is excellent in long-term strength, water tightness, and chemical resistance, and can suppress the heat of hydration and drying shrinkage at the time of curing. In recent years, it has come to be used in large quantities from the viewpoint of effective use.

  On the other hand, when a large amount of fly ash is added to concrete, problems such as setting delay, a decrease in initial strength, and a delay in strength development in a low temperature environment are likely to occur. For this reason, there is an upper limit to the amount of fly ash added. For example, fly ash cements defined in JIS standards limit the replacement rate of fly ash to cement to 30% at maximum, and it is difficult to further increase the amount of fly ash used.

  Moreover, the fluctuation | variation of the quality of fly ash is mentioned as a cause which prevents utilization of fly ash. In other words, in recent years, low-cost, that is, low-grade, multi-variety types of coal have been used to reduce power generation costs at thermal power plants, and the combustion conditions are not the same. Variations in the chemical composition, mineral composition, particle size composition, etc. of the ash are increasing, and these are the causes of fly ash quality fluctuations. Such quality fluctuations may impair the fluidity and strength development of cement containing fly ash.

  As a method for improving the fluidity and strength development of concrete, it has been proposed to optimize the amount of fly ash based on the pH of the fly ash slurry. For example, in Patent Document 1, in a mortar composition or a concrete composition mixed with coal ash (fly ash), when the pH of the slurry liquid containing 20% coal ash is 11.0 or more, cement / coal It has been proposed that the ash ratio (weight ratio) be 0.5 or more.

Japanese Patent Laid-Open No. 9-156971

  However, with conventional cement manufacturing methods, when fly ash is blended, the quality of the cement varies greatly due to variations in the quality of fly ash, making it difficult to stably produce cement having excellent fluidity and strength. Met. For this reason, even if it is a case where the amount of mixing of fly ash is increased, it is calculated | required to establish the technique which can manufacture the cement which has the stably outstanding fluidity | liquidity and strength expression.

  The present invention has been made in view of the above circumstances, and provides a fly ash selection method for selecting, as a cement mixture, fly ash suitable for the production of cement having stable and good strength development. Objective. In addition, by reducing the effect of fly ash quality fluctuation, when fly ash is used as a mixed material, cement, mortar, and cement that can stably produce good strength can be manufactured. An object is to provide a manufacturing method.

  As a result of intensive studies to achieve the above object, the present inventors have found that the BET specific surface area of fly ash and the lattice constant b of α-quartz contained in fly ash are effective as indicators of strength development. The present invention has been completed.

That is, the present invention provides the above α-, which is obtained from one or more types of fly ash containing α-quartz and has a BET specific surface area of 5.0 m ² / g or less as a cement mixture and is obtained by a Rietveld analysis method. A fly ash selection method is provided, wherein a fly ash having a lattice constant b of quartz of 0.4935 nm or less is selected.

In the present invention, by selecting fly ash having a BET specific surface area of 5.0 m ² / g or less and an α-quartz lattice constant b of 0.4935 nm or less, a cement having a stable and good strength development property is selected. Can be manufactured. Since these characteristics can be easily measured, the fly ash selection method of the present invention can be carried out simply and quickly, and is particularly useful in a mass production process.

  In the fly ash selection method of the present invention, it is preferable to select a fly ash having a loss on ignition of 3.00% by mass or less. By selecting fly ash having such characteristics, it is possible to produce a cement having better strength development and good fluidity.

In another aspect, the present invention provides a cement production method for producing cement by mixing Portland cement and fly ash, wherein the BET specific surface area is 5 from one or more fly ash containing α-quartz. .0m and 2 / ^g or less, and lied a selection step of the lattice constant b of the α- quartz sought belt analysis is to select a fly ash or less 0.4935Nm, selected by the Portland cement and the selection process And a mixing step of mixing with the fly ash. A method for producing cement is provided.

The production method of the present invention has a selection step of selecting fly ash having a BET specific surface area of 5.0 m ² / g or less and an α-quartz lattice constant b of 0.4935 nm or less. Cement having good strength development can be produced quickly and stably.

  In the mixing step, 10 to 100 parts by mass of the fly ash selected in the selection step is preferably mixed with 100 parts by mass of the Portland cement. As a result, effective utilization of fly ash is promoted, and a cement having better strength development can be produced.

  According to the fly ash selection method of the present invention, by using the BET specific surface area of fly ash and the lattice constant b of α-quartz in fly ash as selection criteria as indicators of strength development, from a power plant or the like From the obtained fly ash, a fly ash capable of producing a cement excellent in strength development as a cement mixture can be selected easily and quickly. Therefore, according to the method for selecting fly ash of the present invention, it is possible to stably manufacture a cement having good strength development. Moreover, the concrete composition and the mortar composition which have the favorable favorable strength expression can be manufactured using the said cement.

  In addition, according to the present invention, there is provided a method for producing a cement capable of producing a cement having a good strength development property simply, quickly and stably by reducing the influence of quality fluctuations of fly ash. be able to.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

The fly ash selection method of the present embodiment has a BET specific surface area of 5.0 m ² / g or less from fly ash containing one or more kinds of α-quartz and is obtained by a Rietveld analysis method. -Fly ash having a lattice constant b of quartz of 0.4935 nm or less is selected as a cement mixture.

The BET specific surface area of fly ash used for mixing with cement, selected by the fly ash selection method of the present embodiment, is preferably 1.5 to 5.0 m ² / g, more preferably 1.7 to 3. 0.5 m ² / g, more preferably 1.9 to 3.2 m ² / g, and still more preferably 2.4 to 3.2 m ² / g. When the value of this BET specific surface area is less than 1.5 m ² / g, the reactivity of fly ash tends to be low and good strength development tends to be impaired, and when it exceeds 5.0 m ² / g, good strength is obtained. There is a tendency for the expression to be impaired, or the amount of water for obtaining a predetermined fluidity increases, and the shrinkage after curing tends to increase.

  The BET specific surface area of fly ash in this embodiment can be measured using a commercially available gas adsorption device. The BET specific surface area can be determined by applying the BET formula in the range of partial pressure 0.05 to 0.30 to the adsorption isotherm measured by the constant volume method using nitrogen as the measurement adsorption gas. Prior to the measurement, the sample is preferably pretreated by heating at 200 ° C. for 2 hours in a nitrogen atmosphere.

  In the fly ash selection method of this embodiment, a fly ash suitable for obtaining a cement having excellent strength development is selected using the lattice constant b in the crystal structure of α-quartz in fly ash as an index along with the BET specific surface area. To do. That is, an α-quartz lattice constant b of 0.4935 nm or less, preferably 0.4934 nm or less is selected. Accordingly, a suitable fly ash can be selected easily and quickly in order to obtain a cement having good strength development. In addition, although there is no restriction | limiting in particular in the upper limit of the lattice constant b of (alpha) -quartz, From a practical viewpoint, Preferably it is 0.4915 nm or more, More preferably, it is 0.4920 nm or more, More preferably, it is 0.4925 nm or more.

  The lattice constant b of α-quartz contained in fly ash is measured by a Rietveld analysis method using powder X-ray diffraction. The lattice constant b of α-quartz is obtained by converting the total amount of the three phases to 100% by mass with α-quartz (Quartz) and mullite (Mullite) as the quantification target and the rest as amorphous. To calculate. In order to refine the parameters, it is necessary to fix the atomic arrangement of α-quartz and mullite and to make the fitting by changing the profile function, lattice constant, and half width.

  The fly ash used in the selection method of the present embodiment is not limited to that discharged from a coal-fired thermal power plant or the like, and is not particularly limited as long as it is defined in JIS A 6201: 1999 “Fly Ash for Concrete”. Can be used. For example, all coal ash including fluidized bed fly ash can be used.

  The BET specific surface area of fly ash and the lattice constant b of α-quartz vary depending on the fly ash generation conditions. Therefore, in the fly ash selection method of the present embodiment, a plurality of fly ash having different generation conditions are prepared, and the fly ash in which the BET specific surface area and the lattice constant b of the included α-quartz satisfy the numerical range described above. Is preferably selected.

  Further, one type of prepared fly ash is selected into two or more types of fly ash having different average particle diameters using a sieve or the like, and the BET specific surface area and the α-quartz contained therein are selected from the selected fly ash. A fly ash having a lattice constant b satisfying the above numerical range may be selected.

  In the fly ash selection method of the present embodiment, in addition to the above-mentioned BET specific surface area and α-quartz lattice constant b satisfying the above numerical range, the loss on ignition is 3.00% by mass or less. It is preferable to select. The cement obtained by adding the fly ash selected in this way to the cement has stable and good strength development and fluidity. From the same viewpoint, a fly ash having a loss on ignition of more preferably 2.80% by mass or less, and still more preferably 2.60% by mass or less is selected. The ignition loss of fly ash can be measured based on the above JIS A 6201: 1999 “Fly Ash for Concrete”.

  The fly ash selected by the above selection method is used by mixing with Portland cement to obtain a cement that is particularly excellent in strength development. As described above, this selection method is a simple and quick method because the fly ash is selected based on the Rietveld analysis of the BET specific surface area and the powder X-ray diffraction result, and has excellent strength development. Cement can be manufactured easily.

  Next, a preferred embodiment of the cement production method of the present invention will be described.

The method for producing a cement according to the present embodiment is a method for producing a cement by mixing Portland cement and fly ash containing α-quartz, and has a BET specific surface area of 5.0 m ² / g or less. And a selection step of selecting fly ash having a lattice constant b of α-quartz of 0.4935 nm or less determined by the Rietveld analysis method, and the fly selected in the selection step with respect to 100 parts by mass of Portland cement. It has the mixing process which mixes 10-100 mass parts of ash.

In the selection step, the obtained fly ash is selected by the fly ash selection method according to the above embodiment, the BET specific surface area is 5.0 m ² / g or less, and α-quartz of which is obtained by the Rietveld analysis method A fly ash having a lattice constant b of 0.4935 nm or less is selected.

  In the mixing step, 10 to 100 parts by mass of the fly ash selected in the selection step is mixed with 100 parts by mass of Portland cement. Examples of Portland cement include various Portland cements such as ordinary Portland cement, early-strength Portland cement, medium heat Portland cement, and low heat Portland cement. From the viewpoint of increasing the heat of hydration and the strength over the medium to long term, it is preferable to use medium-heated Portland cement.

  When the mixing amount of fly ash with respect to 100 parts by mass of the Portland cement is less than 10 parts by mass, the fluidity tends to decrease, or the reduction of heat of hydration tends to be difficult, and the mixing amount exceeds 100 parts by mass. Then, the setting tends to be delayed, and the strength of the cement at the initial stage of hardening tends to decrease. From the same viewpoint, the amount of fly ash mixed with 100 parts by mass of Portland cement is preferably 20 to 70 parts by mass, more preferably 30 to 60 parts by mass, and even more preferably 40 to 50 parts by mass. In addition, the mixing method in particular of Portland cement and fly ash is not restrict | limited, It can carry out by a well-known method.

  The cement obtained by the production method of the present embodiment is obtained by mixing fly ash selected based on the BET specific surface area and the α-quartz lattice constant b, and thus has excellent strength development. . That is, the cement and concrete and mortar produced using the cement have high strength at the initial stage of curing. In other words, mortar compositions and concrete compositions with excellent strength development can be obtained by adding aggregates such as sand, gravel, and crushed stone used in ordinary concrete or mortar production to the cement obtained by the above-described production method. It can be a thing. As described above, the production method of the present embodiment can easily produce cement, concrete, and mortar having excellent strength development properties, and can add a sufficient amount of fly ash to the cement. It can be said that this is an excellent production method from the viewpoint of effective use of resources.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, in the cement production method of the present invention, for example, blast furnace slag or fine limestone powder may be added in the mixing step.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example and a comparative example, this invention is not limited to an Example.

[Preparation of raw materials]
(cement)
Commercially available moderately hot Portland cement having the chemical composition shown in Table 1 below was prepared.

(Fly ash)
Six types of fly ash 1 to 6 having different properties generated at a coal-fired power plant were prepared. The compositions of fly ash 1 to 6 and the loss on ignition (ig.loss) are shown in Table 2, respectively. The composition is a value measured by powder X-ray diffraction, and the ignition loss is a value measured based on JIS A 6201: 1999 “Fly Ash for Concrete”.

  The BET specific surface areas of fly ash 1 to 6 shown in Table 2 and the lattice constant b (axis length) of α-quartz were as shown in Table 3.

  The BET specific surface area of fly ash 1-6 was measured using a high-accuracy gas adsorption device (trade name: BELSORP-mini, manufactured by Nippon Bell Co., Ltd.). Measured according to “Measurement method”. Specifically, nitrogen was used as the adsorption gas, and the BET formula was applied in the range of partial pressure 0.05 to 0.30 with respect to the adsorption isotherm measured by the constant volume method. The sample was pretreated by heating at 200 ° C. for 2 hours in a nitrogen atmosphere.

  The lattice constant b of each α-quartz contained in fly ash 1-6 was measured using a Rietveld analysis method using powder X-ray diffraction. For measurement of powder X-ray diffraction, a powder X-ray diffraction apparatus RINT-2000 (manufactured by Rigaku Corporation) was used. The measurement was performed using a Cu source with a tube voltage of 35 kV, a tube current of 110 mA, a measurement range of 2θ = 10 to 60 °, a step width of 0.02 °, and a fixed time of 2 seconds. The diverging slit was 1 °, and the light receiving slit was 0.15 mm. For the Rietveld analysis, powder X-ray diffraction pattern comprehensive analysis software (manufactured by Materials Data Inc., trade name: JADE 6.0) was used. In addition, the value described in the reference document shown in Table 4 was used as an initial value of the crystal structure data of α-quartz (Quartz) and mullite (Mullite).

[Reference 1] Kern, A., Eysel., W., Mineralogisch-Petrograph. Inst., Univ. Heidelberg, Germany
[Reference 2] Natl. Bur. Stand. (US) Monogr. 25, v3, p3 (1964)

[Preparation of test cement]
45 parts by mass of various fly ash 1-6 shown in Table 2 (external split) is mixed with 100 parts by mass of moderately hot Portland cement shown in Table 1, and mixed using a rocking mixer, Examples 1-4 And the cements of Comparative Examples 1 and 2 were prepared.

  Using the prepared cements of Examples and Comparative Examples as specimens, mortar compressive strength tests at ages 7 and 28 days were performed based on JIS R 5201: 1997 “Cement physical test method”. The strength development property of was evaluated. Table 5 shows the measurement results of the mortar compressive strength at each age.

As shown in Table 5, the cements of Examples 1 to 4 manufactured by selecting fly ash having a BET specific surface area of 5.0 m ² / g or less and an α-quartz lattice constant b of 0.4935 nm or less, It was confirmed to have good strength development.

Claims (4)

From one or more kinds of fly ash containing α-quartz, the BET specific surface area is 5.0 m ² / g or less as a cement mixture, and the lattice constant b of the α-quartz obtained by the Rietveld analysis method is A method for selecting fly ash, wherein the fly ash is 0.4935 nm or less.   The method for selecting fly ash according to claim 1, wherein the fly ash having an ignition loss of 3.00% by mass or less is selected. A method for producing cement, comprising mixing Portland cement and fly ash to produce cement,
From one or more types of fly ash containing α-quartz, the BET specific surface area is 5.0 m ² / g or less, and the lattice constant b of the α-quartz obtained by Rietveld analysis is 0.4935 nm or less. A selection process for selecting a fly ash,
And a mixing step of mixing the Portland cement and the fly ash selected in the selection step. In the mixing step,
The method for producing cement according to claim 3, wherein 10 to 100 parts by mass of the fly ash is mixed with 100 parts by mass of the Portland cement.